Field of the Invention
The invention relates to apparatus for producing analysis samples for X-ray fluorescence spectroscopy, as well as a method for producing the same.
Discussion of the Prior Art
In X-ray fluorescence spectroscopy, the material to be analyzed is first melted in a crucible and then poured into a casting dish to form what is typically referred to in the field as a “pellet,” “tablet,” “button,” or “bead” that is then used for the analysis. These buttons are typically quite small, about the size of a one-Euro or a two-Euro coin. The equipment is correspondingly small: the crucibles typically have a height of just a few centimeters, for example, approximately 3 to 5 cm, and a similar diameter. Hence, the amount of the material to be melted is in the range of several grams and at most several cubic centimeters. The crucibles could be designated as analysis sample crucibles, but, despite substantial differences to crucibles of the type used in steel mills, foundries, and similar production facilities, the simple term “crucible” is also used for these small crucibles that are used in laboratories for X-ray fluorescence spectroscopy.
The temperatures used to melt the sample materials are very high, ranging from 900 degrees C. to 1400 degrees C. As a result, the equipment obtaining samples for X-ray fluorescence spectroscopy is exposed to high temperature loads.
Crucibles are also used in production industries, for example, in steel mills, in foundries, etc., to produce large and small articles. In these cases, the mass of material to be melted is measured in the range of kilograms and possibly hundreds of kilograms, and the volume in many liters or possibly even cubic liters or cubic meters. The crucibles used for industrial production are typically so large, that they are not placed in the oven at all, but rather, the molten liquid material that is in the oven is poured outside the oven into crucibles or is melted directly in crucibles that are heatable, without the use of an oven. Because these types of crucibles are not placed in an oven, the entire crucible is not designed to be able to withstand the high temperatures that are used in melting operations; instead, just the surface that comes into contact with the molten material is coated with some heat-resistant material, such as a ceramic material. An external metal shell may be provided, but this does not have sufficient resistance to withstand the temperature of the molten material that is in the crucible, and particularly, cannot withstand the temperatures that exist in a melting oven that is used to produce the samples for X-ray fluorescence spectroscopy.
For these reasons, foundry or smelting apparatus that is used in the industrial processing of large volumes of material is, thus, unrelated to apparatus that is used to produce the samples for X-ray fluorescence spectroscopy.
In the production of analysis samples for X-ray fluorescence spectroscopy, the crucible is not setup outside the oven and filled outside the oven with molten sample material, and is also not the type of crucible that has a heat source that heats the sample material directly in the crucible. Rather, the crucible is placed in the oven and is passively heated by the temperature that exists in the oven. Thus, it is essential that a crucible used for analysis samples not just have a fire-resistant coating on the inside of the crucible where the molten material is, but that the entire crucible be able to withstand the high temperatures in the oven. For this reason, crucibles for analysis samples are made entirely of a material that is thermally resistant to the oven temperatures as well as chemically resistant to the sample material. An example of material for such crucibles is platinum or a platinum alloy.
Often in X-ray fluorescence spectroscopy, several crucibles, for example, two, four, or six crucibles, are placed together in one oven. The ovens used for this are often referred to as so-called tabletop devices, because they are so small, they can be placed on a laboratory table, for example. But even if the ovens are set up on the floor or are placed in a rack or cabinet, they are still referred to as tabletop devices, because of their small dimensions.
To produce the button, the molten sample material in the crucible is cast from the crucible into a casting dish. Typically, this operation is carried out inside the oven, in order to minimize the risk that the sample material cools prematurely. The casting dish, which is sometimes also referred to as a mold, is placed in the oven beneath the crucible, and has a concave shape that determines the shape of the button.
Flux or filler is typically added to the sample material as a filler, whereby this flux is frequently in the form of glass. The crucible is set in motion in the oven, in order to thoroughly mix the actual sample material with the filler materials within the crucible.
The use of stirrers in the crucible hasn't proven useful, for a variety of reasons. The conventional method is to set the complete crucible, including its crucible holder and the contents of the crucible, in motion. It is often problematic for practical reasons to do this, because of undesirably high wear on the crucible holder. If such a crucible holder breaks and has to be replaced, then the oven, which may normally have charges of two, four, or six crucibles, cannot be used for the duration of the repair, which results in a significant economic loss.
There are a number of causes for the sensitivity of the conventional crucible holder. For one, the oven used for X-ray fluorescence spectroscopy has an enclosed inner chamber and the temperatures in the oven are very high, as mentioned above. For another, the entire crucible holder with all the crucibles contained in it, is set in motion, in order to mix the sample materials. Also, the crucible holder with all of its crucibles is tiltably supported, so that all the crucibles can simultaneously be poured from the crucibles into the casting dishes beneath the crucibles. This simultaneous emptying is done to avoid a premature and undesired cooling of the samples, and, for this reason, the crucibles are not emptied one after the other.
For these reasons, the crucible used for X-ray fluorescence spectroscopy must satisfy very different conditions than those of crucibles used in industrial production. The conventional apparatus for X-ray fluorescence spectroscopy has lower temperature losses because of the enclosed chamber and, consequently, can be operated more economically and can also be operated with heaters that have a lower heat output than the gas burner that is typically used in industrial applications. Electric heaters, for example, may be used and that is an advantage for safety reasons. Also, the heating effect of a gas burner is concentrated on a small area, for example, on the crucibles. With the conventional X-ray fluorescence spectroscopy apparatus, a significantly more even temperature is provided in the entire closed inner chamber of the oven and, because of this, the crucible holders for the crucibles in X-ray fluorescence spectroscopy are subjected to higher thermal loading. The same applies for the drive elements of the crucible holder that are also provided inside the inner chamber of the oven. These drive elements are used to set the crucible holder along with all its crucibles in motion, the purpose of which is to thoroughly mix the sample materials in the crucibles. Having to repair these crucible holders is a relatively complex task and takes a correspondingly long time, because the oven has to be first cooled down before the crucible holder can be removed.
What is needed, therefore, are apparatus and a method in X-ray fluorescence spectroscopy of loading/unloading an oven that will provide the highest possible productivity level. What is further needed is a crucible holder that is robust enough to withstand the high temperatures of the ovens and has sufficient stability to be placed loosely in the oven. What is yet further needed are apparatus and method for producing samples for X-ray fluorescence spectroscopy with the shortest possible down times and cycle times.